/*
----------------AC自动机+动态规划------------------
利用fail数组的跳转来构造转移方程
 
*/
#include<iostream>
#include<string>
#include<string.h>
#include<vector>
#include<cstdio>
#include<algorithm>
#include<map>
#include<set>
#include<queue>
#include<cmath>
using namespace std;
#define ll long long
#define pi acos(-1)
const int maxn = 1500;


int trie[maxn][26];   //字典树
int color[maxn];   //标记终点
int id;   //当前字典树中有几个节点


int fail[maxn];   //匹配失败时的跳转指针 

int dp[55][maxn];    //dp[i][j]表示长度为i的字符串当前节点是j的最大权值
char s[55][maxn][55];  //s[i][j]表示长度为i当前节点是j的最优字符串解 
char res[55];
 

char word[maxn][15];    //输入的模式串组 


inline void insert(char *ss,int weight)  //将字符串s插入字典树 
{
	int len = strlen(ss);
	int p = 0;  //从0节点开始
	
	for(int i=0;i<len;++i)
	{
		int c = ss[i] - 'a';
		if(!trie[p][c])   //没有边，就加边
		{
			memset(trie[id],0,sizeof(trie[id]));
			color[id] = 0;
			trie[p][c] = id++;	
		}

		p = trie[p][c];
	}
	
	color[p] = weight;
}

inline void getfail()   //利用BFS获取fail数组 
{
	queue<int>q;   //利用BFS获取fail数组 

	for(int i=0;i<26;++i)   //将第二层所有出现了的字母扔进队列
		if(trie[0][i])
		{
			fail[trie[0][i]] = 0;
			q.push(trie[0][i]);
		}
	
	while(!q.empty())
	{
		int u = q.front();
		q.pop();
		
		for(int i=0;i<26;++i)
		{
			if(trie[u][i])
			{
				fail[trie[u][i]] = trie[fail[u]][i];
				q.push(trie[u][i]);
			}
			else
				trie[u][i] = trie[fail[u]][i];
		}
	}
}

inline int search(char *s)  //模式串匹配--只能查出模式串是否出现 
{
	int len = strlen(s);
	int ans = 0;
	int p = 0;
	
	for(int i=0;i<len;++i)
	{
		int c = s[i] - 'a';
		p = trie[p][c];
		
		for(int j=p;j&&color[j]!=-1;j=fail[j])
		{
			//一直向下寻找,直到匹配失败(失败指针指向根或者当前节点已找过
			ans += color[j];
			color[j] = -1;  //将遍历过后的节点标记,防止重复计算
		}
	}
	
	return ans;
}

bool cmp(char *a,char *b)
{
	int len1 = strlen(a);
	int len2 = strlen(b);
	if(len1!=len2) return len1<len2;
	return strcmp(a,b)<0;
}

signed main()
{
	int t;
	int n,m;
	scanf("%d",&t);
	while(t--)
	{
		id = 1;
		memset(trie[0],0,sizeof(trie[0]));
		memset(color,0,sizeof(color));
		
		scanf("%d%d",&n,&m);
		for(int i=1;i<=m;++i) scanf("%s",word[i]);
		
		int weight;
		for(int i=1;i<=m;++i)
		{
			scanf("%d",&weight);
			insert(word[i],weight);
		}
		
		getfail();
		
		memset(dp,-1,sizeof(dp));
		dp[0][0] = 0;
		strcpy(s[0][0],"");
		strcpy(res,"");
		
		char temp[55];
		int temp2 = 0;
		
		for(int i=1;i<=n;++i)
		{
			for(int j=0;j<id;++j)
			{
				if(dp[i-1][j]<0) continue;
				
				strcpy(temp,s[i-1][j]);
				int len = strlen(temp);
				
				for(int k=0;k<26;++k)
				{
					temp[len] = k + 'a';
					temp[len+1] = 0;
					
					int vv = dp[i-1][j] + color[trie[j][k]];
					if(dp[i][trie[j][k]]<vv||dp[i][trie[j][k]]==vv&&cmp(temp,s[i][trie[j][k]]))
					{
						dp[i][trie[j][k]] = vv;
						strcpy(s[i][trie[j][k]],temp);
						if(dp[i][trie[j][k]]>temp2||dp[i][trie[j][k]]==temp2&&cmp(temp,res))
						{
							temp2 = dp[i][trie[j][k]];
							strcpy(res,temp);
						}
					}
				}
			}
		}
		
		printf("%s\n",res);
	}
	return 0;
}
